This section is intended to provide a background or context to the invention that is, inter alia, recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Numerous chemical reactions rely on the use of catalysts to accelerate and control reaction products to achieve commercially useful products, reaction, efficiency, and obtain proper reaction products. For example, catalysts play an important role in polymer electrolyte fuel cell (PEFC) power systems. However, one of the major barriers to the commercialization of PEFC power systems, especially for the automotive application, is cost. The high cost is largely due to the use of platinum-containing electrocatalysts, where the majority of the catalyst is platinum, in the fuel cell electrodes. In the area of polymer electrolyte fuel cell systems the cost of the membrane-electrode assembly system can amount to almost 84% of the total cost of a fuel cell stack and the cost of the anode and cathode are about half that total. While there has been substantial progress recently in reducing the Pt metal loading requirements for the anode and cathode, the cost for the anode and cathode still makes polymer electrolyte fuel cells too expensive for widespread commercial use. The United States Department of Energy has set a target for fuel cell catalyst cost of $5/kW power, with the current status being approximately $25/kW using a platinum cost of $1100/Troy Ounce. Consequently, any further substantial cost reductions, needed to meet the targets for commercial viability, will likely require dramatic improvement of Pt-based catalyst properties or eliminating use of Pt, and using a lower cost metal to improve performance.
Various alternative cathode electrocatalysts for PEFCs, such as non-Pt binary and ternary alloys, early transition metal chalcogenides, macrocycles containing the MN4 moiety, and various transition metal carbides and nitrides have been developed to address this issue.
The Department of Energy has set a goal to achieve a fuel cell cost of $8/kW of power. In addition, the Pt free catalyst must perform at or above Pt activity for oxygen reduction reaction (ORR), and the catalyst must be more stable than Pt in an acidic fuel cell environment. The DOE standards for specific activity, mass activity, volume activity and stability are, respectively, 720 μA/cm2, 0.44 A/mg (@900 mViR-free), >130 A/cm2 (@ 800 mViR-free) and 5,000 hours with potential cycling. The currently available Pt based electrocatalyst not only is extremely costly but also falls short of these technical performance requirements by a factor of two to three.